Transmission system



June 21, 1927.

H. M. B AscoM TRANSMISSION SYSTEM Filed May 8. 1924 frequency 0 In for czrcmz IN VEN TOR L 6 A TTORNEV Patented June 21,1927. I v UNITED STATES .,1'-',e3z,s11 PATENT OFFICE.

I MY I. BASGOI, OF BROOKLYN, NEW YORK, ASSIGNOB TO AMERICAN TELEPHONE AND TELEGBAP HCOMPANY, A CORPORATION OF NEW YORK.

TRANSMISSION SYSTEM.

Application fled Iay a, 1024. Serial a... 711,899.

This invention relates to transmission circuits and more partlcularly to, arrangements for improving the transmission on circuits utilizing the condenser type of transmitter.

An illustration of a circuit arrangement wherein a condenser transmitter might be utilized would be a loud speaker circuit. It has been the practice heretofore to utilize with the condenser transmitter as its source of energy a battery of constant potential. The energy delivered to the receiving circuit from the transmitter with such an arrangement is small due to the very small variation in the electrostatic capacity of the transmitter when subject to sound vibrations. This is an inherent limitation of the condenser transmitter arrangement and it has been the practice to utilize therewith multistage audio-frequency amplifiers. These audio-frequency amplifiers, however, are sub-.

ject to inductive disturbances of audible frequency and hence will amplify the noise as well as the speech and so introduce considerable noise into the receiving circuit. It is in general the purpose of this invention to provide arrangements whereb this noise or inductive disturbance may eliminated from a transmission circuit utilizing a condenser type of transmitter. In the arrangements of the invention this is accomplished by substituting for the battery formerly utilized as the source of energy for the trans.-

mitter an oscillator or source supplying current of super-audio or carrier frequency. The condenser transmitter will be included in a circuit tuned to the frequency supplied from the oscillator and hence will modulate the carrier or inaudible frequency with the speech currents. The amplifiers provided will be adjusted to efficiently amplify the carrier frequency but will not efliciently amplify the inductive disturbances or noises of audible frequenc Hence the noise will not be amplified wit the carrier modulated by the s eech. Associated with the amplifiers may provided high pass filters to pass the carrier frequencies but, which will eliminate any of the noise of audible frequency passed by the amplifiers. A demolulator will be provided at the receiver. With such anarrangement the efliciency of the condenser transmitter may be materially increased and the disturbances or noises introduced in the circuit eliminated. Other features and ob- 't e high frequency current and transmitfrom the following detailed description of 1ts operation.

In the drawing is illustrated a circuit diagram of the arrangements of the invention. A transmission line is shown comprising an oscillator circuit 1. The oscillator circuit is shown as a vacuum tube oscillator arrangement but any source of high frequency oscillations might be employed which will generate oscillations of a frequency above the limits of audibility. The oscillator circuit 1 is associated by transformer. 3 with the transmitter circuit 2 in which is included a condenser transmitter 4. Circuit 2 is'tuned to be resonant to the frequency of the oscillations supplied from circuit 1. The sound vibrations impressed on transmitter 4 will vary its electrostatic capacity and hence change the tuning of circuit 2. This will have the effect of modulating the high frequency current from source 1 with the speech vibrations. The modulated high frequency current will be transmitted to, circuit 5 which may include amplifying apparatus illustrated schematically as 6. The amplifiers-6 will be adjusted to efiiciently amplify the high frequency modulated current which is above the limits of audibility but will not efficiently amplify any inductive disturbances or noises within the audible range. In the output of the amplifiers 6 may be provided a high pass filter illustrated schematically as 7 which will readily allow the transmission of currents of the order of the modulated high frequency currents but which will attenuate and practically extinguish currents within the audible limits which might be transmitted by amplifiers 6,suc h as currents due to inductive disturbance. The high frequency currents modulated by the speech Wlll then be transmitted to circuit 8 which will include a demodulator, illustrated as the vacuum tube device 9. The s eech component will then be taken off ted to a circuit 10 which may'include receiv- 'in apparatus. With this arrangement the e ciency of the condenser type of transmitter may be materially increased and the noises or disturbances transmitted to the receiving circuit may be greatly reduced.

While the invention has been disclosed in certain specific arrangements which are deemed desirable, it is understood that it is jects of the invention will appear more fully capable of embodiment in many and widely cuit whereby varied forms without de arting from the spirit of the invention as efined by the appended claim.

What is claimed is:

A transmission line comprising a source of high frequency oscillations above the ordinary telephonic range, a circuit associated with said source and tuned to be resonant at the frequency of said oscillations, a condenser transmitter associated with said cirthe resonance of said circuit may be varied as the electrostatic capacity of said transmitter varies, an amplifier associated with said circuit and adjusted to efiiciently amplify said high frequency oscillations, a filter associated with the out ut of said amplifier and adapted to rea ily transmit said high frequency oscillations and to attenuate frequencies within said telephonic range, and demodulating apparatus 20 IIENRY M. BASCOM. 

